Spectral and photophysical properties of fluorone dyes in bio-related films and methanol

The fluorone dyes fluorescein, 4,5-dibromofluorescein, eosin Y, erythrosine B, and rose bengal in the biological materials gelatin, starch, and chitosan have been characterized by absorption and emission spectroscopy. Comparative studies were carried out for the same dyes in methanol. The absorption cross-section spectra, luminescence quantum distributions, luminescence quantum yields, fluorescence quantum yields, and degrees of luminescence polarization were determined by steady-state spectroscopy. The fluorescence lifetimes were measured by time-resolved laser experiments. High fluorescence quantum yields were obtained for fluorescein in both the solid hosts and the liquid solutions. The fluorescence reduction due to enhancement of intersystem crossing by heavy atom spin-orbit coupling was efficient both in the biofilms and in methanol. Room temperature phosphorescence emission was observed for the heavy atom substituted fluorescein derivatives in the biofilms. The spectroscopic behavior of the fluorone dyes depends on their ionic state with highest luminescence efficiency for the dianionic forms. This form was realized for all investigated dyes in basic methanol and in most cases also in the biofilms.